1. Field of the Invention
The present invention relates to an image forming device such as a copy machine, a printer and a facsimile machine in which a removable developing unit is used for adhering a developer on an electrostatic latent image and developing the electrostatic latent image.
2. Description of the Related Art
In an image forming device, when carrying out an image forming process by adhering a developer (toner) onto an electrostatic latent image carrier on which an electrostatic latent image is formed, a remaining amount of the developer decreases with the use of the developer in the image forming process. Therefore, it is necessary to replenish the developer as needed. Thus, the developing unit is formed capable of being inserted and removed with respect to the image forming device. When necessary, the developing unit is removed from the image forming device and the developer is replenished or the developing unit is replaced. However, if the developing unit is not positioned properly with respect to the electrostatic latent image carrier, the developer is not adhered evenly on the electrostatic latent image carrier and unevenness is generated in the image forming process.
In consideration to such drawbacks, for example, according to a first conventional image forming device, two pressure rollers are provided at both ends of a developing sleeve, respectively. A transferring direction of the pressure rollers is regulated by a pair of regulatory members having a surface parallel to a straight line that connects centers of a photoconductive drum and the developing sleeve. The pressure rollers are pressured toward the photoconductive drum by an elastic member such as a spring. According to a second conventional image forming device, gap rollers are provided at both ends of a developing roller to provide an interval between a surface of a photoconductive drum and an axial center of the developing roller at a prescribed interval.
According to the first conventional image forming device, the moving direction of the pressure rollers is regulated by the pair of regulatory members and the developing sleeve is positioned. However, since a pressure force for the photoconductive drum is applied to the pressure rollers, if a positional relationship between the regulatory members and the pressure rollers is not set precisely, a positional relationship between the photoconductive drum and the developing sleeve is displaced and the developer cannot be moved evenly from the developing sleeve to the photoconductive drum. Moreover, according to the method to press the pressure rollers directly and to contact the pressure rollers against a surface of the photoconductive drum, an excessive force is applied to the pressure rollers and there are cases in which the positioning cannot be carried out properly. According to the second conventional image forming device, since there is a possibility for the gap rollers to be displaced from the photoconductive drum, a structure for accurately positioning the gap rollers with respect to the surface of the photoconductive drum becomes necessary.
In the above-described image forming device, a detecting unit is provided for detecting a remaining amount of the toner in a developing unit. When the remaining amount of the toner becomes small, an alarm is generated. However, since the developing unit is inserted and removed with respect to the device frame, the detecting unit provided in the device frame is necessary to be set at a detection position when the developing unit is inserted.
As a method for solving such drawbacks, for example, according to a third conventional image forming device, a toner remaining amount detecting unit made of a transparent member is attached on a side surface of a developing unit. A concave groove of the toner remaining amount detecting unit is inserted between a light emitter and a light receiver provided in a device frame. According to a fourth conventional image forming device, in response to opening and closing movements of a cover, a sensor holder is swung. Under a state in which the cover is opened, the sensor holder is swung against an urging spring so as to release a contacting state between a magnetic toner sensor and a developer container. Under a state in which the cover is closed, the magnetic toner sensor makes contact with the developer container by an urging force of the urging spring.
In the third conventional image forming device, there is no problem when inserting the developing unit from an upper side of the device frame. However, it is difficult to insert the developing unit from a lateral side. The developing unit cannot be inserted easily unless a gap is spaced to some degree. However, if there is a gap, after the developing unit is inserted, the developing unit jounces and cannot be positioned accurately. Furthermore, for the developing unit to be inserted easily, it is necessary to increase the size of the concave groove of the toner remaining amount detecting unit. However, an available volume in the developing unit is reduced by a volume of the concave groove and an amount of the toner that can be accumulated becomes small.
In the fourth conventional image forming device, since the magnetic toner sensor makes contact with an outer surface of the container, an optical sensor cannot be used. In addition, since the surface of the container is pressed by the urging spring, it is necessary to increase the strength of the container.